Late Eocene Ostracoda (Crustacea) from the Waihao district, South Canterbury, New Zealand

Abstract

A well-preserved and diverse ostracod fauna of late Eocene, Kaiatan Stage age is described from a mudstone sample (Ashley Mudstone Formation) from the Waihao River outcrop near McCulloch's Bridge, South Canterbury, New Zealand. A total of 8,662 specimens are assigned to 104 species including one new genus and 13 new species. Of the new species all but the Cytheruridae are described herein. The new genus is Taracythere, type species T. proterva (Hornibrook, 1953) and the new species described here are: Pseudeucythere biplana, Eucythere sulcocostatula, Copytus pseudoelongatus, Neocytherideis reticulata, Patagonacythere waihaoensis, Munseyella pseudobrevis, Actinocythereis microagrenon and Pennyella leptodictyota. Because of a need for reillustration of established species, most of the remaining 91 species are illustrated and the systematics of some of these is remarked upon. Sixty-two species have been previously described, eight are tentatively referred to previously described species, and 21 are left in open nomenclature mainly due to paucity of material. The assemblage is interpreted as having lived in a low energy marine environment on the outer shelf or upper slope. Comparison with contempory ostracod faunas of southeastern Australia indicates very high affinity: 56 common genera, out of the 61 genera listed here. Considering the timing of Tasman seafloor spreading (Paleocene to Middle Eocene) and foundering of continental crustal regions of the eastern Tasman Basin to bathyal depths (initially Middle Eocene), trans-Tasman ostracod dispersal probably predates late Eocene times. The greater number of endemic Eocene genera recorded in Australia suggests that migration was dominantly eastwards.